Compatible television system with companding of auxiliary signal encoding information

ABSTRACT

An NTSC compatible, single channel widescreen EDTV system encodes and decodes a television signal comprising (1) a main, standard format NTSC signal wth auxiliary low frequency side panel image information compressed into an overscan region thereof; (2) auxiliary high frequency side panel image information; and (3) auxiliary high frequency horizontal luminance information. High frequency components 2 and 3 are subjected to non-linear amplitude companding, with large amplitude compression at an encoder and inverse amplitude expansion at a decoder.

BACKGROUND OF THE INVENTION

This invention concerns apparatus for companding non-standard televisionsignal encoding information. In particular, this invention concerns suchapparatus employed by a system for generating a widescreen televisionsignal which is compatible with a standard television signal receiver.

A conventional television receiver, such as a receiver in accordancewith NTSC broadcast standards adopted in the United States andelsewhere, has a 4:3 aspect ratio (the ratio of the width to the heightof a displayed image). Recently, there has been interest in using higheraspect ratios for television receiver systems, such as 2:1, 16:9 or 5:3,since such higher aspect ratios more nearly approximate or equal theaspect ratio of the human eye than does the 4:3 aspect ratio of aconventional television receiver. Video information signals with a 5:3aspect ratio have received particular attention since this ratioapproximates that of motion picture film, and thus such signals can betransmitted and received without cropping the image information.However, widescreen television systems which simply transmit signalshaving an increased aspect ratio as compared to conventional systems areincompatible with conventional aspect ratio receivers. This makeswidespread adoption of widescreen systems difficult.

It is therefore desirable to have a widescreen system which iscompatible with conventional television receivers. One such system isdisclosed in a copending U.S. patent application Ser. No. 078,150 of C.H. Strolle et al., titled "Compatible Widescreen Television System",filed July 27, 1987. It is even more desirable to have such a compatiblewidescreen system with provisions for enhancing or extending thedefinition of the displayed image so as to provide extra image detail.For example, such widescreen EDTV (extended definition television)system may include apparatus for providing a progressively scannedimage.

In a compatible widescreen system, it may be necessary to transmitauxiliary video information together with existing standard information,e.g., in frequency interleaved form. It is desirable to convey suchinformation via an auxiliary signal or signals with a large amplitude soas to enhance the signal-to-noise ratio of the auxiliary information.However, a large amplitude auxiliary signal can lead to unwantedinterference with the standard video information intended to beprocessed by a standard receiver. Thus, one is faced with the dilemma ofusing a large amplitude auxiliary signal to maintain a goodsignal-to-noise ratio, or using a small amplitude auxiliary signal toprevent interference with standard video information. This dilemma isresolved in accordance with the principles of the present invention.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, certainauxiliary information is divided into low and high frequency portions.The high frequency portion is subjected to a non-linear companding(compression/expansion) process for large amplitude excursions.Compression is performed at an encoder, e.g., at a transmitter, andcomplementary expansion is performed at a decoder, e.g., at a receiver.

In accordance with a feature of the invention, the low frequencyinformation of the auxiliary signal is time compressed into an imageoverscan region at an encoder, and time expanded by a decoder. Thus theauxiliary information is subjected to both a time companding process andan amplitude companding process.

In accordance with a further feature of the invention, the highfrequency non-linear companding process is disclosed in the context of asingle channel widescreen extended definition television (EDT) system,e.g., a high resolution progressive scanning pro-scan system, that iscompatible with a standard television receiver.

In a disclosed preferred embodiment of a compatible widescreen EDTVtelevision system in accordance with the principles of the presentinvention, an original high resolution, progressively scanned widescreensignal is encoded to include four components derived from a compositesignal. The four components are processed separately before beingrecombined in a single signal transmission channel.

A first component is a main 2:1 interlaced signal with a standard 4:3aspect ratio. This component comprises a central portion of thewidescreen signal that has been time expanded to occupy nearly theentire 4:3 aspect ratio active line time, and side panel horizontal lowfrequency information that has been time compressed into the left andright horizontal image overscan regions where such information is hiddenfrom view in a standard television receiver display.

A second component is an auxiliary 2:1 interlaced signal comprising leftand right side panel high frequency information that have each been timeexpanded to half the active line time. Thus expanded side panelinformation occupies substantially the entire active line time. Largeamplitude excursions of this high frequency signal are subjected to acompanding process with nonlinear amplitude compression at the encoderand complementary expansion at the decoder.

A third component is an auxiliary 2:1 interlaced signal, derived fromthe widescreen signal source, comprising high frequency horizontalluminance detail information between approximately 5.0 MHz and 6.2 MHz.Large amplitude excursions of this high frequency signal are subjectedto a companding process with nonlinear amplitude compression at theencoder and complementary expansion at the decoder.

A fourth component is an auxiliary 2:1 interlaced "helper" signalcomprising vertical-temporal (V-T) luminance detail information thatwould otherwise be lost in the conversion from progressive scan tointerlaced format. This signal component helps to reconstruct missingimage information and to reduce or eliminate unwanted flicker and motionartifacts at a widescreen EDTV receiver.

At a widescreen EDTV receiver, a composite signal containing thedescribed four components is decoded into the constituent fourcomponents. The decoded components are processed separately and used todevelop an image representative widescreen signal with enhancedresolution.

The disclosed widescreen EDTV system offers several significantimprovements over a standard NTSC system. The wider aspect ratio, withthe visible impact of motion picture film, is immediately apparent. Thewidescreen picture is "quieter", virtually free from the interlineflicker so common in standard NTSC receiver displays. The picture isalso "cleaner", virtually free from "crawling dots", "hanging dots" anddisturbing rainbow color effects. The widescreen picture has noticeablyincreased resolution in both spatial dimensions. Line structure is notvisible because of the increased line density. In moving portions of thepicture, absent are annoying beats between moving horizontal edges andthe scanning structure.

DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a general overview of a compatible widescreen EDTVencoder system in accordance with the present invention;

FIG. 1a shows a detailed block diagram of the encoder for the disclosedsystem;

FIGS. 1b-1e contain diagrams helpful in understanding the operation ofthe disclosed system;

FIGS. 2-5 depict signal waveforms and diagrams helpful in understandingthe operation of the disclosed system;

FIG. 13 shows a block diagram of a portion of a widescreen EDTV receiverincluding decoder apparatus in accordance with the present invention;and

FIGS. 6-12 and 14-24 illustrate aspects of the disclosed system ingreater detail.

A system intended to transmit wide aspect ratio pictures, e.g., 5:3,through a standard, e.g., NTSC, broadcast channel should achieve a highquality picture display by a widescreen receiver, while greatly reducingor eliminating observable degradations in a standard 4:3 aspect ratiodisplay. The use of signal compression techniques on the side panels ofa picture takes advantage of the horizontal overscan region of astandard NTSC television receiver display, but may sacrifice imageresolution in the side panel regions of a reconstructed widescreenpicture. Since compression in time results in an expansion in thefrequency domain, only low frequency components would survive processingin a standard television channel, which exhibits a smaller bandwidthcompared with that required for a widescreen signal. Thus, when thecompressed side panels of a compatible widescreen signal are expanded ina widescreen receiver, there results a noticeable difference between theresolution or high frequency content of the center portion of adisplayed widescreen picture and the side panels, unless steps are takento avoid this effect. This noticeable difference is due to the fact thatlow frequency side panel information would be recovered, but highfrequency information would be lost due to video channel bandlimitingeffects.

In the system of FIG. 1, elements which are common to the more detailedsystem of FIG. 1a are identified by the same reference number. As shownin FIG. 1, an original widescreen progressive-scan signal with left,right and center panel information is processed so as to develop fourseparate encoding components. These four components were describedabove, and are illustrated generally in FIG. 1 in the context of animage display. Processing of the first component (containing timeexpanded center portion information and time compressed side portion lowfrequency information) is such that the resulting luminance bandwidthdoes not exceed the NTSC luminance bandwidth of 4.2 MHz in this example.This signal is color encoded in standard NTSC format, and the luminanceand chrominance components of this signal are suitably pre-filtered(e.g., using field comb filters) to provide improvedluminance-chrominance separation at both standard NTSC and widescreenreceivers.

The time expansion of the second component (side panel high frequencyinformation) reduces its horizontal bandwidth to about 1.1 MHz. Thiscomponent is spatially uncorrelated with the main signal (the firstcomponent), and special precautions are taken to mask its visibility onstandard NTSC receivers, as will be discussed.

The 5.0 to 6.2 MHz extended high-frequency luminance information contentof the third component is first shifted downward in frequency to afrequency range of 0 to 1.2 MHz before further processing. Thiscomponent is mapped into the standard 4:3 format, which spatiallycorrelates it with the main signal (the first component) to mask itsvisibility on standard NTSC receivers. The compressed side panelinformation of the third component exhibits a bandwidth which isone-sixth that of the center information (0-1.2 MHz).

The fourth component (vertical-temporal helper) is mapped into standard4:3 format to correlate it with the main signal component to therebymask its visibility on standard NTSC receivers and is horizontallybandwidth limited to 750 KHz.

The first, second, and third components are processed by respectiveintraframe averagers 38, 64, and 76 (a type of vertical-temporal (V-T)filter) to eliminate V-T crosstalk between the main and auxiliary signalcomponents at a widescreen receiver. The first component is intra-frameaveraged only above approximately 1.5 MHz. The second and thirdintraframe averaged components, identified as X and Z, are non-linearlyamplitude compressed prior to quadrature modulating a 3.108 MHzalternate subcarrier ASC, having a field alternating phase unlike achrominanace subcarrier, in a block 80. A modulated signal (M) fromblock 80 is added to the intraframe averaged first component (N) in anadder 40. A resulting output signal is a 4.2 MHz bandwidth basebandsignal (NTSCF) that, together with a 750 KHz low pass filtered fourthcomponent (YTN) from a filter 79, quadrature modulates an RF picturecarrier in a block 57 to produce an NTSC compatible RF signal which canbe transmitted to a standard NTSC compatible RF or a widescreenprogressive scan receiver via a single, standard bandwith, broadcastchannel.

As will be seen from the encoder of FIG. 1a, the use of time compressionon the first component allows low frequency side panel information to besqueezed entirely into the horizontal overscan region of a standard NTSCsignal. The high frequency side panel information is spectrally sharedwith the standard NTSC signal through the video transmission channel, ina manner transparent to a standard receiver, through the use of analternate subcarrier quadrature modulation technique involving block 80as will be discussed. When received by a standard NTSC receiver, onlythe center panel portion of the main signal (the first component) isseen. The second and third components may create a low amplitudeinterference pattern that is not perceived at normal viewing distanceand at normal picture control settings. The fourth component is removedcompletely in receivers with synchronous video detectors. In receiverswith envelope detectors, the fourth component is processed but notperceived because it is correlated with the main signal.

FIG. 1b illustrates the RF spectrum of the disclosed EDTV widescreensystem, including the auxiliary information, compared to the RF spectrumof a standard NTSC system. In the spectrum of the disclosed system theside panel highs and the extra high frequency horizontal luminancedetail information extend approximately 1.1 MHz on either side of the3.108 MHz alternate subcarrier (ASC) frequency. The V-T helper signalinformation (component 4) extends 750 KHz on either side of the mainsignal picture carrier frequency.

A widescreen progressive scan receiver includes apparatus forreconstructing the original widescreen progressive scan signal. Comparedto a standard NTSC signal, the reconstructed widescreen signal has leftand right side panels with standard NTSC resolution, and a 4:3 aspectratio center panel with superior horizontal and vertical luminancedetail particularly in stationary portions of an image.

Two basic considerations govern the signal processing techniqueassociated with the development and processing of the first, second,third, and fourth signal components. These considerations arecompatibility with existing receivers, and recoverability at thereceiver.

Full compatibility implies receiver and transmitter compatibility suchthat-existing standard receivers can receive widescreen EDTV signals andproduce a standard display without special adaptors. Compatibility inthis sense requires, for example, that the transmitter image scanningformat is substantially the same as, or within the tolerance of, thereceiver image scanning format. Compatibility also means that extranon-standard components must be physically or perceptually hidden in themain signal when displayed on standard receivers. To achievecompatibility in the latter sense, the disclosed system uses thefollowing techniques to hide the auxiliary components.

As discussed above, the side panel lows are physically hidden in thenormal horizontal overscan region of a standard receiver. Component 2,which is a low-energy signal compared to the side panel lows component,and component 3, which is a normally low energy high frequency detailsignal, are amplitude compressed and quadrature modulated onto analternate subcarrier at 3.108 MHz, which is an interlaced frequency (anodd multiple of one-half the horizontal line rate). The frequency,phase, and amplitude of the alternate subcarrier are chosen so that thevisibility of the modulated alternate subcarrier signal is reduced asmuch as possible, e.g., by controlling the phase of the alternatesubcarrier from to field to field so that it alternates 180° from onefield to the next, unlike the phase of the chrominance subcarrier fromone field to the next. Although the modulated alternate subcarriercomponents reside entirely within the chrominance passband (2.0-4.3MHz), the modulated alternate subcarrier components are perceptuallyhidden because they are displayed as field rate complementary colorflicker, which is not perceived by the human eye at normal levels ofchrominance saturation. Also, nonlinear amplitude compression of themodulation components prior to amplitude overshoots to an acceptablelower level. Component 3 is hidden by time expanding the center panelinformation to match the standard 4:3 format, thereby spatiallycorrelating (and temporarily correlating) component 3 with component 1.This is accomplished by means of a format encoder as will be discussed.Such spatial correlation helps to prevent the component 3 informationform interfering with the component 1 information after component 3 isquadrature modulated with component 2 on the alternate subcarrier andcombined with component 1.

Component 4, the "helper" signal, also is hidden by time expanding thecenter panel information to match the standard 4:3 format, therebyspatially correlating component 4 with the main signal. Component 4 isremoved at standard receivers with synchronous detectors, and isperceptually hidden at standard receivers with envelope detectorsbecause it is spatially correlated with the main signal.

Recovery of components 1, 2, and 3 at a widescreen progressive scanreceiver is accomplished by utilizing a process of intraframe averagingat the transmitter and receiver. This process is associated withelements 38, 64, and 76 in the transmitter system of FIGS. 1 and 1a, andwith associated elements at the receiver as will be discussed.Intraframe averaging is one type of signal conditioning technique whichprepares two highly visually correlated signals for mutual combining sothat they can be recovered efficiently and accurately afterwards, suchas by means of a field storage device, free from V-T (vertical-temporal)crosstalk even in the presence of motion in the case of imagerepresentative signals. The type of signal conditioning employed forthis purpose essentially involves making two signals identical on afield basis, i.e., by obtaining two samples with identical values afield apart. Intraframe averaging is a convenient technique forachieving this objective, but other techniques can also be used.Intraframe averaging is basically a linear, time varying digitalpre-filtering and post-filtering process to ensure the accurate recoveryof two highly visually correlated combined signals. Horizontal crosstalkis eliminated by guardbands between horizontal pre-filters at thetransmitter encoder and post-filters at the receiver decoder.

The process of intraframe averaging in the time domain is illustratedgenerally by FIG. 1c, wherein pairs of fields are made identical byaveraging pixels (A, B and C,D) that are 262H apart. The average valuereplaces the original values in each pair. FIG. 1d illustrates theprocess of intraframe averaging in the context of the system of FIG. 1.Starting with components 2 and 3, pairs of pixels (picture elements)262H apart within a frame are averaged, and the average value (e.g., X1,X3 and Z1, Z3) replaces the original pixel values. This V-T averagingoccurs within a frame and does not cross frame boundaries. In the caseof component 1, intraframe averaging is performed only on informationabove approximately 1.5 MHz so as not to affect lower frequency verticaldetail information. In the case of components 1 and 2, intraframeaveraging is performed on a composite signal including luminance (y) andchrominance (c) components throughout the chrominance band. Thechrominance component of the composite signal survives intraframeaveraging because pixels 262H apart are "in-phase" with respect to thecolor subcarrier the phase of the new alternate subcarrier is controlledso that it is exactly out of phase for pixels 262H apart, and thus has aphase unlike that of a chrominance subcarrier. Thus when components 2and 3 (after quadrature modulation) are added to component 1 in unit 40,pixels 262H apart have the form (M+A) and (M-A), where M is a sample ofthe main composite signal above 1.5 MHz, and A is a sample of theauxiliary modulated signal.

With intraframe averaging V-T crosstalk is virtually eliminated, even inthe presence of motion. In this regard, the process of intraframeaveraging produces identical samples 262H apart. At the receiver it is asimple matter to recover the information content of these samplesexactly, i.e., free from crosstalk, by averaging and differencing pixelsamples 262H apart within a frame as will be discussed, therebyrecovering main and auxiliary signal information. At a recoder in thereceiver, the intraframe averaged original information can be recoveredsubstantially intact via an intraframe averaging and differencingprocess since the original information is highly visually correlatedfield-to-field.

Also at the receiver, the RF channel is quadrature demodulated using asynchronous RF detector. Component 4 is thereby separated from the otherthree components. Intraframe averaging and differencing are used toseparate component 1 from modulated components 2 and 3, as will bediscussed with regard to FIG. 13.

After the four components have been recovered, the composite signals areNTSC decoded and separated into luminance and chrominance components.Inverse mapping is performed on all components to recover the widescreenaspect ratio, and the side panel highs are combined with the lows torecover full side panel resolution. The extended high frequencyluminance detail information is shifted to its original frequency rangeand added to the luminance signal, which is converted to the progressivescan format using temporal interpolation and the helper signal. Thechrominance signal is converted to progressive scan format usingunassisted temporal interpolation. Finally, the luminance andchrominance progressive scan signals are converted to analog form andmatrixed to produce RGB color image signals for display by a widescreenprogressive scan display device.

Before discussing the compatible widescreen encoding system of FIG. 1a,reference is made to signal waveforms A and B of FIG. 2. Signal A is a5:3 aspect ratio widescreen signal that is to be converted to a standardNTSC compatible signal with a 4:3 aspect ratio as depicted by signal B.Widescreen signal A includes a center panel portion associated withprimary image information occupying an interval TC, and left and rightside panel portions associated with secondary image information andoccupying intervals TS. In this example the left and right side panelsexhibit substantially equal aspect ratios, less than that of the centerpanel which is centered therebetween.

Widescreen signal A is converted to NTSC signal B by compressing certainside panel information completely into the horizontal overscan regionsassociated with time intervals TO. The standard NTSC signal has anactive line interval TA (approximately 52.5 microseconds duration) whichencompasses overscan intervals TO, a display time interval TD whichcontains the video information to be displayed, and a total horizontalline time interval TH of approximately 63.556 microseconds duration.Intervals TA and TH are the same for both the widescreen and thestandard NTSC signals. It has been found that almost all consumertelevision receivers have an overscan interval which occupies at least4% of the total active line time TA, i.e., 2% overscan on the left andright sides. At an interlace sampling rate of 4×fsc (where fsc is thefrequency of the color subcarrier), each horizontal line intervalcontains 910 pixels (picture elements) of which 754 constitute theactive horizontal line image information to be displayed.

The widescreen EDTV system is shown in greater detail in FIG. 1a.Referring to FIG. 1a, a 525 line, 60 field/sec. widescreen progressivescan camera 10 provides a widescreen color signal with R, G, Bcomponents and a wide aspect ratio of 5:3 in this example. An interlacedsignal source could also be used, but a progressive scan signal sourceproduces superior results. A widescreen camera has a greater aspectratio and a greater video bandwidth compared to a standard NTSC camera,the video bandwidth of a widescreen camera being proportional to theproduct of its aspect ratio and the total number of lines per frame,among other factors. Assuming constant velocity scanning by thewidescreen camera, an increase in its aspect ratio causes acorresponding increase in its video bandwidth as well as horizontalcompression of picture information when the signal is displayed by astandard television receiver with a 4:3 aspect ratio. For these reasons,it is necessary to modify the widescreen signal for full NTSCcompatibility.

The color video signal processed by the encoder system of FIG. 1contains both luminance and chrominance signal components. The luminanceand chrominance signals contain both low and high frequency information,which in the following discussion will be referred to as "lows" and"highs", respectively.

The wide bandwidth widescreen progressive scan color video signals fromcamera 10 are matrixed in a unit 12 to derive luminance component Y andcolor difference signal components 1 and Q from the R, G, B colorsignals. Wideband progressive scan signals Y, I, Q are sampled at aneight-times chrominance subcarrier rate (8×fsc), and are converted fromanalog to digital (binary) form individually by separateanalog-to-digital converters (ADC) in an ADC unit 14 before beingfiltered individually by separate vertical-temporal (V-T) low passfilters in a filter unit 16 to produce filtered signals YF, IF and QF.These signals are each of the form indicated by waveform A in FIG. 2.The separate filters are 3×3 linear time invariant filters of the typeshown in FIG. 10d as will be discussed. These filters reducevertical-temporal resolution slightly, particularly diagonal V-Tresolution, to prevent unwanted interlace artifacts (such as flicker,jagged edges, and other aliasing related effects) in the main signal(component 1 in FIG. 1) after progressive scan to interlace conversion.The filters maintain nearly full vertical resolution in stationaryportions of the image.

The center panel expansion factor (CEF) is a function of the differencebetween the width of an image displayed by a widescreen receiver and thewidth of an image displayed by a standard receiver. The image width of awidescreen display with a 5:3 aspect ratio is 1.25 times greater thanthe image width of a standard display with a 4:3 aspect ratio. Thisfactor of 1.25 is a preliminary center panel expansion factor which mustbe adjusted to account for the overscan region of a standard receiver,and to account for an intentional slight overlap of the boundary regionsbetween the center and side panels as will be explained. Theseconsiderations dictate a CEF of 1:19.

The progressive scan signals from filter network 16 exhibit a bandwidthof 0-14.32 MHz and are respectively converted into 2:1 interlacedsignals by means of progressive scan (P) to interlace (I) converters17a, 17b and 17c, details of which will be discussed in connection withFIGS. 22 and 23. The bandwidth of output signals IF', QF' and YF' fromconverters 17a-17c exhibit a bandwidth of 0-7.16 MHz since thehorizontal scanning rate for interlaced signals is half that ofprogressive scan signals. In the conversion process, the progressivescan signal is subsampled, taking half the available pixel samples toproduce the 2:1 interlaced main signal. Specifically, each progressivescan signal is converted to 2:1 interlaced format by retaining eitherthe odd or even lines in each field and reading out the retained pixelsat a 4×fsc rate (14.32 MHz). All subsequent digital processing of theinterlaced signals occurs at the 4×fsc rate. In a progressively scannedsystem a complete image, an image frame, is produced by each completevertical image scan. In an interlaced system, a complete image isproduced by a combination of two successive interlaced vertical fieldscans which together constitute an image frame.

Network 17c also includes an error prediction network. One output ofnetwork 17c, YF', is the interlaced subsampled luminance version of theprefiltered progressive scan component. Another output (luminance)signal of network 17c, YT, comprises vertical-temporal informationderived from image frame difference information and represents atemporal prediction, or temporal interpolation, error between actual andpredicted values of luminance samples "missing" at the receiver, as willbe explained. The prediction is based on a temporal average of theamplitudes of "before" and "after" pixels, which are available at thereceiver. Signal YT, a luminance "helper" signal that assists toreconstruct the progressive scan signal at the receiver, essentiallyaccounts for an error that the receiver is expected to make with respectto non-stationary image signals and facilitates cancellation of sucherror at the receiver. In stationary portions of an image the error iszero, and perfect reconstruction is performed at the receiver. It hasbeen found that a chrominance helper signal is not needed as a practicalmatter, and that a luminance helper signal is sufficient to produce goodresults since the human eye is less sensitive to a lack of chrominancevertical or temporal detail. FIG. 2a illustrates the algorithm used todevelop helper signal YT.

Referring to FIG. 2a, pixels A, X, and B in the progressive scan signaloccupy the same spatial position in an image. Black pixels such as A andB are transmitted as the main signal and are available at the receiver.A white pixel, such as X, is not transmitted and is predicted by atemporal frame average (A+B)/2. That is, at the encoder a prediction ismade for "missing" pixel X by averaging the amplitudes of "before" and"after" pixels A and B. The prediction value, (A+B)/2, is subtractedfrom the actual value, X to produce a prediction error signal,corresponding to the helper signal, with an amplitude in accordance withthe expression X-(A+B)/2. This expression defines temporal framedifference information components (X-A)/2+(X-B)/2, which may also beexpressed as (X-A)/2-(B-X)/2. The helper signal is lowpass filteredhorizontally by means of a 750 KHz low pass filter and conveyed ashelper signal YT. Bandlimiting of the helper signal to 750 KHz isnecessary to prevent this signal from interfering with the next lower RFchannel after this signal is modulated onto the RF picture carrier. Atthe receiver, a similar prediction of missing pixel X is made by usingan average of samples A and B, and the prediction error is added to theprediction. That is, X is recovered by adding the prediction errorX-(A+B)/2 to the temporal average (A+B)/2. Thus the V-T helper signalfacilitates the conversion from interlaced to progressive scan format.

The helper signal produced by the disclosed temporal predictionalgorithm advantageously is a low energy signal compared to a predictionsignal produced by some other algorithms, such as that used to produce aline differential signal as described by M. Tsinberg in an article"ENTSC Two-Channel Compatible HDTV System", IEEE Transactions onConsumer Electronics, Vol. CE-33, No. 3, August 1987, pp. 146-153. Instill areas of an image, the error energy is zero because the predictionis perfect. A low energy condition is manifested by still andsubstantially still images (such as a news broadcast featuring areporter against a still background). The disclosed algorithm has beenfound to produce the least objectionable artifacts after imagereconstruction at the receiver, and the helper signal produced by thedisclosed algorithm retains its usefulness after being bandlimited(filtered) to about 750 KHz. The helper signal produced by the disclosedalgorithm advantageously exhibits zero energy in the presence of stillimage information, and consequently a helper signal associated with astill image is unaffected by filtering. A highly improved reconstructedwidescreen image results even if the helper signal is not transmitted.In such case still portions of the image will be much sharper than astandard NTSC image, but moving portions will be somewhat "softer" andmay exhibit a "beat" artifact. Thus a broadcaster need not transmit thehelper signal initially, but can choose to upgrade the RF transmissionat a later time.

The disclosed temporal prediction system is useful for both progressivescan and interlaced systems with higher than standard line rates, butworks best with a progressive scan source having pixels A, X and Boccupying the same spatial position in an image, which results in aperfect prediction for still images. The temporal prediction will beimperfect even in still portions of an image if the original widescreenimage comes from an interlaced signal source. In such case the helpersignal will have more energy and will introduce slight artifacts instill portions of a reconstructed image. Experiments have shown that theuse of an interlaced signal source yields acceptable results withartifacts being noticeable only upon close inspection, but that aprogressive scan signal source introduces fewer artifacts and producespreferred results.

Returning to FIG. 1a, interlaced widescreen signals IF', QF' and YF'from converters 17a-17c are respectively filtered by horizontal lowpassfilters 19a, 19b and 19c to produce a signal IF" with a bandwidth of0-600 KHz, a signal QF" with a bandwidth of 0-600 KHz, and a signal YF"with a bandwidth of 0-5 MHz. These signals are next subjected to aformat encoding process which encodes each of these signals into a 4:3format by means of format encoding apparatus associated with aside-center signal separator and processor unit 18. Briefly, the centerportion of each widescreen line is time-expanded and mapped into thedisplayed portion of the active line time with a 4:3 aspect ratio. Timeexpansion causes a decrease in bandwidth so that the original widescreeninterlaced frequencies are made compatible with the standard NTSCbandwidth. The side panels are split into horizontal frequency bands sothat the I and Q color highs component exhibit a bandwidth of 83 KHz-600KHz (as shown for signal IH in FIG. 7) and the Y luminance highscomponent exhibits a bandwidth of 700 KHz-5.0 MHz (as shown for signalYH in FIG. 6). The side panel lows, i.e., signals YO, IO and QOdeveloped as shown in FIGS. 6 and 7, include a DC component and aretime-compressed and mapped into the left and right horizontal imageoverscan regions on each line. The side panel highs are processedseparately. Details of this format encoding process follow immediatelybelow.

In the course of considering the following encoding details, it will behelpful to also consider FIG. 1e, which depicts the process of encodingcomponents 1, 2, 3 and 4 in the context of displayed center and sidepanel information. Filtered interlaced signals IF", QF" and YF" areprocessed by side-center panel signal separator and processor 18 toproduce three groups of output signals: YE, IE and QE; YO, IO and QO;and YH, IH and QH. The first two groups of signals (YE, IE, QE and YO,IO, QO) are processed to develop a signal containing a full bandwidthcenter panel component, and side panel luminance lows compressed intohorizontal overscan regions. The third group of signals (YH, IH, QH) isprocessed to develop a signal containing side panel highs. When thesesignals are combined, an NTSC compatible widescreen signal with 4:3display aspect ratio is produced. Details of circuits comprising unit 18will be shown and discussed in connection with FIGS. 6, 7 and 8.

Signals YE, IE and QE contain complete center panel information andexhibit the same format, as indicated by signal YE in FIG. 3. Briefly,signal YE is derived from signal YF" as follows. Widescreen signal YF"contains pixels 1-754 occurring during the active line interval of thewidescreen signal, containing side and center panel information. Thewideband center panel information (pixels 75-680) is extracted as acenter panel luminance signal YC via a time de-multiplexing process.Signal YC is time expanded by the center panel expansion factor of 1.19(i.e., 5.0 MHz÷4.2 MHz) to produce NTSC compatible center panel signalYE. Signal YE exhibits an NTSC compatible bandwidth (0-4.2 MHz) due tothe time expansion by factor 1.19. Signal YE occupies picture displayinterval TD (FIG. 2) between overscan regions TO. Signals IE and QE aredeveloped from signals IF" and QF", respectively, and are similarlyprocessed in the manner of signal YE.

Signals YO, IO and QO provide the low frequency side panel information("lows") which is inserted into the left and right horizontal overscanregions. Signals YO, IO and QO exhibit the same format, as indicated bysignal YO in FIG. 3. Briefly, signal YO is derived from signal YF" asfollows. Widescreen signal YF contains left panel information associatedwith pixels 1-84 and right panel information associated with pixels671-754. As will be discussed, signal YF" is low pass filtered toproduce a luminance lows signal with a 0-700 KHz bandwidth, from whichsignal a left and right side panel lows signal is extracted (signal YL'in FIG. 3) via a time de-multiplexing process. Luminance lows signal YL'is time compressed to produce side panel lows signal YO with compressedlow frequency information in the overscan regions associated with pixels1-14 and 741-754. The compressed side lows signal exhibits an increasedBW proportional to the amount of time compression. Signals IO and QO aredeveloped from signals IF" and QF" respectively, and are similarlyprocessed in the manner of signal YO.

Signals YE, IE, QE and YO, IO, QO are combined by a side-center signalcombiner 28, e.g. a time multiplexer, to produce signals YN, IN and QNwith an NTSC compatible bandwidth and a 4:3 aspect ratio. These signalsare of the form of signal YN shown in FIG. 3. Combiner 28 also includesappropriate signal delays for equalizing the transit times of thesignals being combined. Such equalizing signal delays are also includedelsewhere in the system as required to equalize signal transit times.

A modulator 30, bandpass filter 32, H-V-T bandstop filter 34 andcombiner 36 constitute an improved NTSC signal encoder 31. Chrominancesignals IN and QN are quadrature modulated on a subcarrier SC at theNTSC chrominance subcarrier frequency, nominally 3.58 MHz, by modulator30 to produce a modulated signal CN. Modulator 30 is of conventionaldesign and will be described in connection with FIG. 9. Modulated signalCN is bandpass filtered in the vertical (V) and temporal (T) dimensionsby means of two-dimensional (V-T) filter 32, which removes crosstalkartifacts in the interlaced chrominance signal before it is applied to achrominance signal input of combiner 36 as a signal CP. Luminance signalYN is bandstop filtered in the horizontal (H), vertical (V) and temporal(T) dimensions by means of three-dimensional H-V-T bandstop filter 34before being applied, as a signal YP, to a luminance input of combiner36. Filtering luminance signal YN and chrominance color differencesignals IN and QN serves to assure that luminance-chrominance crosstalkwill be significantly reduced after subsequent NTSC encoding.Multi-dimensional spatial-temporal filters such as H-V-T filter 34 andV-T filter 32 in FIG. 1 comprise structure as illustrated by FIG. 10which will be discussed subsequently.

H-V-T bandstop filter 34 in FIG. 1a exhibits the configuration of FIG.10b, and removes upwardly moving diagonal frequency components fromluminance signal YN. These frequency components are similar inappearance to chrominance subcarrier components and are removed to makea hole in the frequency spectrum into which modulated chrominance willbe inserted. The removal of the upwardly moving diagonal frequencycomponents from luminance signal YN does not visibly degrade a displayedpicture because it has been determined that the human eye issubstantially insensitive to these frequency components. Filter 34exhibits a cut-off frequency of approximately 1.5 MHZ so as not toimpair luminance vertical detail information.

V-T bandpass filter 32 reduces the chrominance bandwidth so thatmodulated chrominance side panel information can be inserted into thehole created in the luminance spectrum by filter 34. Filter 32 reducesthe vertical and temporal resolution of chrominance information suchthat static and moving edges are slightly blurred, but this effect is oflittle or no consequence due to the insensitivity of the human eye tosuch effect.

An output center/side lows signal C/SL from combiner 36 contains NTSCcompatible information to be displayed, as derived from the center panelof the widescreen signal, as well as compressed side panel lows (bothluminance and chrominance) derived from the side panels of thewidescreen signal and situated in the left and right horizontal overscanregions not seen by a viewer of an NTSC receiver display. The compressedside panel lows in the overscan region represent one constituent part ofthe side panel information for a widescreen display. The otherconstituent part, the side panel highs, is developed by processor 18 aswill be discussed below. Side panel high signals YH (luminance highs),IH (I highs) and QH (Q highs) are illustrated by FIG. 4. FIGS. 6, 7 and8 illustrate apparatus for developing these signals, as will bediscussed. In FIG. 4, signals YH, IH and QH contain left panel highfrequency information associated with left panel pixels 1-84, and rightpanel high frequency information associated with right panel pixels671-754.

Signal C/SL is processed by an intraframe averager 38 to produce asignal N, which is applied to an input of an adder 40. Intraframeaveraged signal N is essentially identical to signal C/SL because of thehigh visual correlation of intraframe information of signal C/SL.Averager 38 averages signal C/SL above approximately 1.5 MHz and assiststo reduce or eliminate vertical-temporal crosstalk between the main andauxiliary signals. The highpass frequency range of 1.5 MHz and aboveover which intraframe averager 38 operates was chosen to assure thatfull intraframe averaging is accomplished for information at 2 MHz andabove, to prevent luminance vertical detail information from beingdegraded by the process of intraframe averaging. Horizontal crosstalk iseliminated by means of a 200 KHz guardband between a filter associatedwith intraframe averager 38 in encoder 31 and a filter associated withan intraframe averager-differencer . unit in the decoder of FIG. 13.FIGS. 11a and 11b show details of highs intraframe averager 38. FIGS.11a, 11b and 13 will be discussed subsequently.

Signals IH, QH, and YH are placed in NTSC format by means of an NTSCencoder 60 which is similar to encoder 1. Specifically, encoder 60includes apparatus of the type shown in FIG. 9, as well as apparatus forquadrature modulating side panel chrominance highs information onto theside panel luminance highs information at 3.58 MHz, to produce signalNTSCH, the side panel highs information in NTSC format. This signal isillustrated by FIG. 5.

The use of multi-dimensional bandpass filtering in NTSC encoders 31 and60 advantageously permits the luminance and chrominance components to beseparated virtually free of crosstalk at the receiver when the receiverincludes complementary multi-dimensional filtering for separating theluminance and chrominance information. The use of complementary filtersfor luminance/chrominance encoding and decoding is called cooperativeprocessing and is discussed in detail in an article by C. H. Strolletitled "Cooperative Processing for Improved Chrominance/LuminanceSeparation", published in the SMPTE Journal, Vol. 95, No. 8, August1986, pp. 782-789. Even standard receivers using conventional notch andline-comb filters will benefit from the use of such multi-dimensionalpre-filtering at the encoder by exhibiting reduced chrominance/luminancecrosstalk.

Signal NTSCH is time expanded by a unit 62 to produce an expanded sidehighs signal ESH. Specifically, as shown in FIG. 5, the expansion isaccomplished by a "mapping" process which maps left side panel pixels1-84 of signal NTSCH into pixel positions 1-377 of signal ESH, i.e., theleft side highs of signal NTSCH are expanded to occupy one half the linetime of signal ESH. The right side panel portion (pixels 671-754) ofsignal NTSCH is similarly processed. The time expansion process reducesthe horizontal bandwidth of the information comprising signal ESH(compared to that of signal NTSCH) by a factor of 377/84. The mappingprocess by which time expansion is accomplished can be realized byapparatus of the type shown and to be discussed in connection with FIGS.12-12d. Signal ESH is intra-frame averaged by a network 64, of the typeshown in FIG. 11b, to produce a signal X as illustrated in FIG. 5.Intraframe averaged signal X is essentially identical to signal ESH,because of the high visual correlation of intraframe image informationof signal ESH. Signal X is applied to a signal input of a quadraturemodulator 80.

Signal YF' is also filtered by a horizontal bandpass filter 70 with apassband of 5 MHz-6.2 MHz. The output signal from filter 70, horizontalluminance highs, is applied to an amplitude modulator 72 where itamplitude modulates a 5 MHz carrier signal f_(c). Modulator 72 includesan output low pass filter with a cut-off frequency of approximately 1.2MHz to obtain a signal with a 0-1.2 MHz passband at the output ofmodulator 72. The upper (aliased) sideband (5.0-6.2 MHz) produced by themodulation process is removed by the 1.2 MHz lowpass filter.Effectively, horizontal luminance highs frequencies in the range 5.0MHz-6.2 MHz have been shifted to the range 0-1.2 MHz as a result of theamplitude modulation process and subsequent low pass filtering. Thecarrier amplitude should be large enough so that the original signalamplitudes are retained after filtering by the 1.2 MHz low pass filter.That is, a frequency shift without affecting amplitude is produced.

The frequency-shifted horizontal luminance highs signal from unit 72 isencoded by means of a format encoder 74 to spatially correlate thissignal with the main signal, C/SL. Encoder 74 is similar to formatencoding networks associated with units 18 and 28 for the purpose ofexpanding the center panel information and compressing the side panellows information into the horizontal overscan region. That is, encoder74 encodes the frequency shifted horizontal luminance highs into astandard 4:3 format using techniques that will be discussed inconnection with FIGS. 6-8. When the center portion of the input signalto encoder 74 is time expanded, its bandwith drops to approximately 1.0MHz from 1.2 MHz, and the output signal from encoder 74 becomesspatially correlated with the main signal. The side panel information islowpass filtered within unit 72 to 170 KHz before being time-compressedby encoder 74. The signal from encoder 74 is intraframe averaged bymeans of apparatus 76 similar to that illustrated in FIG. 11b, beforebeing applied to unit 80 as signal Z. Intraframe averaged signal Z isessentially identical to the signal from encoder 74 because of the highvisual correlation of intraframe image information of the signal fromencoder 74. Modulating signal X, a composite signal containing luminanceand chrominance information, and modulating signal Z exhibitsubstantially the same bandwith, approximately 0-1.1 MHz.

As will be discussed in connection with FIG. 24, unit 80 performsnonlinear gamma function amplitude compression on large amplitudeexcursions of the two auxiliary signals, X and Z, before these signalsquadrature modulate an alternate subcarrier signal ASC. A gamma of 0.7is used, whereby the absolute value of each sample is raised to the 0.7power and multiplied by the sign of the original sample value. Gammacompression reduces the visibility of potentially interfering largeamplitude excursions of the modulated signals on existing receivers, andallows predictable recovery at the widescreen receiver since the inverseof the gamma function employed at the encoder is predictable and can bereadily implemented at the receiver decoder.

The amplitude compressed signals are then quadrature modulated on a3.1075 MHz phase-controlled alternate subcarrier ASC, which is an oddmultiple of one half the horizontal line frequency (395×H/2). The phaseof the alternate subcarrier is caused to alternate 180° from one fieldto the next, unlike the phase of the chrominance subcarrier. The fieldalternating phase of the alternate subcarrier permits the auxiliarymodulating information of signals X and Z to overlap chrominanceinformation and produces complementary phased auxiliary informationcomponents A1, -A1 and A3, -A3 of the modulated auxiliary signal, whichfacilitates the separation of the auxiliary information using arelatively uncomplicated field storage device at the receiver. Thequadrature modulated signal, M, is added to signal N in adder 40. Theresulting signal, NTSCF, is a 4.2 MHz NTSC compatible signal.

The described non-linear gamma function employed in the encoder for thepurpose of large amplitude compression is a constituent part of anon-linear companding (compression-expansion) system which also includesa complementary gamma function in the decoder of a widescreen receiverfor the purpose of amplitude expansion, as will be discussedsubsequently. The disclosed non-linear companding system has been foundto significantly reduce the impact of auxiliary non-standard informationupon the standard image information, without causing visible degradationof an image due to noise effects. The companding system uses anon-linear gamma function to instantaneously compress large amplitudeexcursions of auxiliary, non-standard widescreen high frequencyinformation at the encoder, with a complementary non-linear gammafunction being used to correspondingly expand such high frequencyinformation at the decoder. The result is a reduction in the amount ofinterference with existing standard video information caused by largeamplitude auxiliary high frequency information, in the disclosedcompatible widescreen system wherein non-standard auxiliary widescreeninformation is split into low and high frequency portions subjected tocompanding. At the decoder, non-linear amplitude expansion of thecompressed high frequency information does not result in excessiveperceived noise since large amplitude high frequency information istypically associated with high contrast image edges, and the human eyeis insensitive to noise at such edges. The described companding processbetween the alternate reduces cross modulation products between thealternate subcarrier and the chrominance subcarrier, with associatedreduction in visible beat products.

Luminance helper signal YT exhibits a bandwidth of 7.16 MHz and isencoded into the 4:3 format (in the same manner as accomplished byencoder 74, e.g., of the type shown in FIG. 6) by means of a formatencoder 78, and is horizontally lowpass filtered to 750 KHz by a filter79 to produce a signal YTN. The side portions are lowpass filtered to125 KHz before time compression by means of an input lowpass filter offormat encoder 78, corresponding to input filter 610 of the apparatusshown in FIG. 6 but with a cut-off frequency of 125 KHz. The sideportion highs are discarded. Thus signal YTN is spatially correlatedwith main signal C/SL.

Signals YTN and NTSCF are converted from digital (binary) to analog formby means of DAC units 53 and 54 respectively, before these signals areapplied to an RF quadrature modulator 57 for modulating a TV RF carriersignal. The RF modulated signal is afterwards applied to a transmitter55 for broadcast via an antenna 56.

Alternate subcarrier ASC associated with modulator 80 is horizontallysynchronized and has a frequency chosen to insure adequate separation(e.g., 20-30 db.) of side and center information, and to haveinsignificant impact upon an image displayed by a standard NTSCreceiver. The ASC frequency preferably should be an interlace frequencyat an odd multiple of one half the horizontal line rate so as not toproduce interference which would compromise the quality of a displayedpicture.

Quadrature modulation such as provided by unit 80 advantageously permitstwo narrowband signals to be transmitted simultaneously. Time expandingthe modulating highs signals results in a bandwidth reduction,consistent with the narrowband requirements of quadrature modulation.The more the bandwidth is reduced, the less likely it is thatinterference between the carrier and modulating signals will result.Furthermore, the typically high energy DC component of the side panelinformation is compressed into the overscan region rather than beingused as a modulating signal. Thus the energy of the modulating signal,and therefore the potential interference of the modulating signal, aregreatly reduced.

The encoded NTSC compatible widescreen signal broadcast by antenna 56 isintended to be received by both NTSC receivers and widescreen receivers,as illustrated by FIG. 13.

In FIG. 13, a broadcast compatible widescreen EDTV interlaced televisionsignal is received by an antenna 1310 and applied to an antenna input ofan NTSC receiver 1312. Receiver 1312 processes the compatible widescreensignal in normal fashion to produce an image display with a 4:3 aspectratio, with the widescreen side panel information being in partcompressed (i.e., "lows") into the horizontal overscan regions out ofsight of the viewer, and being in part (i.e., "highs") contained in themodulated alternate subcarrier signal which does not disrupt thestandard receiver operation.

The compatible widescreen EDTV signal received by antenna 1310 is alsoapplied to a widescreen progressive scan receiver 1320 capable ofdisplaying a video image with a wide aspect ratio of, e.g., 5:3. Thereceived widescreen signal is processed by an input unit 1322 includingradio frequency (RF) tuner and amplifier circuits, a synchronous videodemodulator (a quadrature demodulator) which produces a baseband videosignal, and analog-to-digital (ADC) converter circuits for producing abaseband video signal (NTSCF) in binary form. The ADC circuits operateat a sampling rate of four times the chrominance subcarrier frequency(4×fsc).

Signal NTSCF is applied to an intraframe averager-differencer unit 1324which averages (additively combines) and differences (subtractivelycombines) image lines 262H apart within frames, above 1.7 MHz, torecover main signal N and quadrature modulated signal M substantiallyfree from V-T crosstalk. A 200 KHz horizontal crosstalk guardband isprovided between the 1-7 MHz lower limit operating frequency of unit1324 and the 1.5 MHz lower limit operating frequency of unit 38 in theencoder of FIG. 1a. Recovered signal N contains information which isessentially visually identical to image information of main signal C/SL,due to the high visual intraframe image correlation of original mainsignal C/SL as intraframe averaged in the encoder of FIG. 1a.

Signal M is coupled to a quadrature demodulator and amplitude expanderunit 1326 for demodulating auxiliary signals X and Z in response to analternate subcarrier ASC with a field alternating phase, similar tosignal ASC discussed in connection with FIG. 1a. Demodulated signals Xand Z contain information which is essentially visually identical toimage information of signal ESH and of the output signal from unit 74 inFIG. 1a, due to the high visual intraframe image correlation of thesesignals as intraframe averaged by the encoder of FIG. 1a. Unit 1326 alsoincludes a 1.5 MHz lowpass filter to remove unwanted high frequencydemodulation products at twice the alternate subcarrier frequency, andan amplitude expander for expanding the (previously compressed)demodulated signals using an inverse-gamma function (gamma=1/0.7=1.429),i.e., the inverse of the non-linear compression function performed byunit 80 in FIG. 1a.

A unit 1328 time compresses the color encoded side panel highs so thatthey occupy their original time slots, thereby recovering signal NTSCH.Unit 1328 time compresses signal NTSCH by the same amount that unit 62of FIG. 1a time expanded signal NTSCH.

A luminance (Y) highs decoder 1330 decodes luminance horizontal highssignal Z into widescreen format. The sides are time expanded (by thesame amount as sides time compression in the encoder of FIG. 1a), andthe center is time compressed (by the same amount as sides timeexpansion in the encoder of FIG. 1a). The panels are spliced together inthe 10-pixel overlap region as will be explained subsequently inconnection with FIG. 14. Unit 1330 is arranged as shown in FIG. 17.

Modulator 1332 amplitude modulates the signal from decoder 1330 on a 5.0MHz carrier f_(c). The amplitude modulated signal is afterwards highpass filtered by a filter 1334 with a 5.0 Mhz cut-off frequency toremove the lower sideband. In the output signal from filter 1334, centerpanel frequencies of 5.0 to 6.2 MHz are recovered, and side panelfrequencies of 5.0 to 5.2 MHz are recovered. The signal from filter 1334is applied to an adder 1336.

Signal NTSCH from compressor 1328 is applied to a unit 1340 forseparating the luminance highs from the chrominance highs to producesignals YH, IH and QH. This can be accomplished by the arrangement ofFIG. 18.

Signal N from unit 1324 is separated into its constituent luminance andchrominance components YN, IN and QN by means of a luminance-chrominanceseparator 1342 which can be similar to separator 1340 and which canemploy apparatus of the type shown in FIG. 18.

Signals YH, IH, QH and YN, IN, QN are provided as inputs to a Y-I-Qformat decoder 1344, which decodes the luminance and chrominancecomponents into widescreen format. The side panel lows are timeexpanded, the center panel is time compressed, the side panel-highs areadded to the side panel lows, and the side panels are spliced to thecenter panel in the 10-pixel overlap region using the principles of FIG.14. Details of decoder 1344 are shown in FIG. 19.

Signal YF' is coupled to adder 1336 where it is summed with the signalfrom filter 1334. By this process recovered extended high frequencyhorizontal luminance detail information is added to decoded luminancesignal YF'.

Signals YF', IF' and QF' are converted from interlaced to progressivescan format by means of converters 1350, 1352 and 1354, respectively.Luminance progressive scan converter 1350 also responds to "helper"luminance signal YT from a format decoder 1360, which decodes encoded"helper" signal YTN. Decoder 1360 decodes signal YTN into widescreenformat, and exhibits a configuration similar to that of FIG. 17.

I and Q converters 1352 and 1354 convert interlace to progressive scansignals by temporally averaging lines one frame apart to produce themissing progressive scan line information. This can be accomplished byapparatus of the type shown in FIG. 20.

Luminance progressive scan converter unit 1350 is similar to that shownin FIG. 20, except that signal YT is added as shown by the arrangementof FIG. 21. In this unit a "helper" signal sample, YT, is added to atemporal average to assist reconstructing a missing progressive scanpixel sample. Full temporal detail is recovered within the band ofhorizontal frequencies contained in the encoded line difference signal(750 KHz, after encoding). Above this band of horizontal frequenciessignal YT is zero, so the missing sample is reconstructed by temporalaveraging.

Widescreen progressive scan signals YF, IF and QF are converted toanalog form by means of a digital-to-analog converter 1362 before beingapplied to a video signal processor and matrix amplifier unit 1364. Thevideo signal processor component of unit 1364 includes signalamplifying, DC level shifting, peaking, brightness control, contrastcontrol and other conventional video signal processing circuits. Matrixamplifier 1364 combines luminance signal YF with color differencesignals IF and QF to produce color image representative video signals R,G and B. These color signals are amplified by display driver amplifiersin unit 1364 to a level suitable for directly driving a widescreen colorimage display device 1370, e.g. a widescreen kinescope.

FIG. 6 illustrates apparatus included in processor 18 of FIG. 1a fordeveloping signals YE, YO, and YH from wideband widescreen signal YF.Signal YF" is horizontally low pass filtered by an input filter 610 witha cutoff frequency of 700 KHz to produce low frequency luminance signalYL, which is applied to one input of a subtractive combiner 612. SignalYF" is applied to another input of combiner 612 and to timede-multiplexing apparatus 616 after being delayed by a unit 614 tocompensate for the signal processing delay of filter 610. Combiningdelayed signal YF" and filtered signal YL produces high frequencyluminance signal YH at the output of combiner 612.

Delayed signal YF" and signals YH and YL are applied to separate inputsof de-multiplexing apparatus 616, which includes de-multiplexing (DEMUX)units 618, 620 and 621 for respectively processing signals YF", YH andYL. The details of de-multiplexing apparatus 616 will be discussed inconnection with FIG. 8. De-multiplexing units 618, 620 and 621respectively derive full bandwidth center panel signal YC, side panelhighs signal YH and side panel lows signal YL' as illustrated in FIGS. 3and 4.

Signal YC is time expanded by a time expander 622 to produce signal YE.Signal YC is time expanded with a center expansion factor sufficient toleave room for the left and right horizontal overscan regions. Thecenter expansion factor (1.19) is the ratio of the intended width ofsignal YE (pixels 15-740) to the width of signal YC (pixels 75-680) asshown in FIG. 3.

Signal YL' is compressed with a side compressing factor by a timecompressor 628 to produce signal YO. The side compression factor (6.0)is the ratio of the width of

the corresponding portion of signal YL' (e.g. left pixels 1-84) to theintended width of signal YO (e.g. left pixels 1-14) as shown in FIG. 3.Time expanders 622, 624 and 626 and time compressor 628 can be of thetype shown in FIG. 12, as will be discussed.

Signals IE, IH, IO and QE, QH, QO are respectively developed fromsignals IF" and QF" in a manner similar to that by which signals YE, YHand YO are developed by the apparatus of FIG. 6. In this regardreference is made to FIG. 7, which illustrates apparatus for developingsignals IE, IH and IO from signal IF". Signals QE, QH and QO aredeveloped from signal QF" in a similar manner.

In FIG. 7, wideband widescreen signal IF", after being delayed by a unit714, is coupled to de-multiplexing apparatus 716 and is alsosubtractively combined with low frequency signal IL from a low passfilter 710 in a subtractive combiner 712 to produce high frequencysignal IH. Delayed signal IF" and signals IH and IL are respectivelyde-multiplexed by de-multiplexers 718, 720 and 721 associated withde-multiplexing apparatus 716 to produce signals IC, IH and IL'. SignalIC is time expanded by an expander 722 to produce signal IE, and signalIL' is time compressed by a compressor 728 to produce signal IO. SignalIC is expanded with a center expansion factor similar to that employedfor signal YC as discussed, and signal IL' is compressed with a sidecompression factor similar to that employed for signal YL', also asdiscussed.

FIG. 8 illustrates a de-multiplexing apparatus 816 such as can be usedfor apparatus 616 of FIG. 6 and 716 of FIG. 7. The apparatus of FIG. 8is illustrated in the context of de-multiplexer 616 of FIG. 6. Inputsignal YF" contains 754 pixels defining the image information. Pixels1-84 define the left panel, pixels 671-754 define the right panel, andpixels 75-680 define the center panel which overlaps the left and rightpanels slightly. Signals IF" and QF" exhibit similar overlap. As will bediscussed, such panel overlap has been found to facilitate combining(splicing) the center and side panels at the receiver to substantiallyeliminate boundary artifacts.

De-multiplexing apparatus 816 includes first, second and thirdde-multiplexer (DEMUX) units 810, 812 and 814 respectively associatedwith left, center and right panel information. Each de-multiplexer unithas an input "A" to which signals YH, YF" and YL are respectivelyapplied, and an input "B" to which a blanking signal (BLK) is applied.The blanking signal may be a logic 0 level or ground, for example. Unit810 extracts output signal YH, containing the left and right highs, frominput signal YH as long as a signal select input (SEL) of unit 810receives a first control signal from a count comparator 817 indicatingthe presence of left panel pixel elements 1-84 and right panel pixelelements 671-754. At other times, a second control signal from countcomparator 817 causes the BLK signal at input B rather than signal YH atinput A to be coupled to the output of unit 810. Unit 814 and a countcomparator 820 operate in a similar fashion for deriving side panel lowssignal YL' from signal YL. Unit 812 couples signal YF" from its input Ato its output to produce center panel signal YC only when a controlsignal from a count comparator 818 indicates the presence of centerpanel pixels 75-680.

Count comparators 817, 818 and 820 are synchronized to video signal YF"by means of a pulse output signal from a counter 822 which responds to aclock signal at four times the chrominance subcarrier frequency (4×fsc),and to a horizontal line synchronizing signal H derived from videosignal YF". Each output pulse from counter 822 corresponds to a pixelposition along a horizontal line. Counter 822 exhibits an initial offsetof a -100 count corresponding to the 100 pixels from the beginning ofthe negative going horizontal sync pulse at time T_(HS) to the end ofthe horizontal blanking interval, at which time pixel 1 appears at theonset of the horizontal line display interval. Thus counter 822 exhibitsa count of "1" at the onset of the line display interval. Other counterarrangements can also be developed. The principles employed byde-multiplexing apparatus 816 can also be applied to multiplexingapparatus for performing a converse signal combining operation, such asis performed by side-center panel combiner 28 in FIG. 1a.

FIG. 9 shows details of modulator 30 in encoders 31 and 60 of FIG. 1a.In FIG. 9, signals IN and QN appear at a four times chrominancesubcarrier rate (4×fsc) and are applied to signal inputs of latches 910and 912, respectively. Latches 910 and 912 also receive 4×fsc clocksignals to transfer in signals IN and QN, and a 2×fsc switching signalwhich is applied to an inverting switching signal input of latch 910 andto a noninverting switching signal input of latch 912. Signal outputs oflatches 910 and 912 are combined into a single output line at whichsignals I and Q appear alternately and are applied to signal inputs of anoninverting latch 914 and an inverting latch 916. These latches areclocked at a 4×fsc rate and receive a switching signal, at thechrominance subcarrier frequency fsc, at inverting and noninvertinginputs respectively. Noninverting latch 914 produces an outputalternating sequence of positive polarity signals I and Q, and invertinglatch 916 produces an output alternating sequence of negative polarity Iand Q signals, i.e. -I, -Q. The outputs of latches 914 and 916 arecombined in a single output line on which appears an alternatingsequence of paired I and Q signals of mutually opposite polarity pairs,i.e., I, Q, -I, -Q . . . etc., constituting signal CN. This signal isfiltered by filter 32 before being combined in unit 36 with a filteredversion of luminance signal YN to produce NTSC encoded signal C/SL ofthe form Y+I, Y+Q, Y-I, Y-Q, Y+I, Y+Q . . . and so on.

FIG. 10 illustrates a vertical-temporal (V-T) filter which can exhibitV-T bandpass, V-T bandstop or V-T low pass configurations by adjustingweighting coefficients a1-a9. The table of FIG. 10a illustrates theweighting coefficients associated with V-T bandpass and bandstop filterconfigurations which are employed in the disclosed system. An H-V-Tbandstop filter such as filter 34 of FIG. 1a, and H-V-T bandpass filterssuch as are included in the decoder system of FIG. 13, respectivelycomprise the combination of a horizontal lowpass filter 1020 and a V-Tbandstop filter 1021 as shown in FIG. 10b, and the combination of ahorizontal bandpass filter 1030 and a V-T bandpass filter 1031 as shownin FIG. 10C.

In the H-V-T bandstop filter of FIG. 10b, horizontal lowpass filter 1020exhibits a given cut-off frequency and provides a filtered low frequencysignal component. This signal is subtractively combined in a combiner1023 with a delayed version of the input signal from a delay unit 1022to produce a high frequency signal component. The low frequencycomponent is subjected to a one frame delay by means of a network 1024before being applied to an additive combiner 1025 for providing an H-V-Tbandstop filtered output signal. V-T filter 1021 exhibits the V-Tbandstop filter coefficients shown in FIG. 10a. An H-V-T bandpass filtersuch as included in the decoder of FIG. 13 is shown in FIG. 10c ascomprising a horizontal bandpass filter 1030 having a given cut-offfrequency, cascaded with a V-T bandpass filter 1031 having V-T bandpassfilter coefficients as indicated by the table of FIG. 10a.

The filter of FIG. 10 includes a plurality of cascaded memory units (M)1010a-1010h for providing successive signal delays at respective tapst1-t9, and for providing an overall filter delay. Signals conveyed bythe taps are respectively applied to one input of multipliers1012a-1012i. Another input of each of the multipliers respectivelyreceives a prescribed weighting a1-a9 depending on the nature of thefiltering process to be performed. The nature of the filtering processalso dictates the delays imparted by memory units 1010a-1010h.Horizontal dimension filters employ pixel storage memory elements suchthat the overall filter delay is less than the time interval of onehorizontal image line (1H). Vertical dimension filters employ linestorage memory elements exclusively, and temporal dimension filtersemploy frame storage memory elements exclusively. Thus an H-V-T 3-Dfilter comprises a combination of pixel, (<1H), line (1H) and frame(>1H) storage elements, while a V-T filter comprises only the latter twotypes of memory elements. Weighted tapped (mutually delayed) signalsfrom elements 1012a-1012i are combined in an adder 1015 to produce afiltered output signal.

Such filters are non-recursive, finite impulse response (FIR) filters.The nature of the delay provided by the memory elements depends on thetype of signal being filtered and the amount of crosstalk that can betolerated between the luminance, chrominance and side panel highssignals in this example. The sharpness of the filter cutoffcharacteristics is enhanced by increasing the number of cascaded memoryelements.

FIG. 10d illustrates one of the separate filters of network 16 in FIG.1a, including cascaded memory (delay) units 1040a-1040d, associatedmultipliers 1042a-1042e with designated respective weighting factorsa1-a5 for receiving signals from signal taps t1-t5, and a signalcombiner 1045 which sums the weighted output signals from multipliersa1-a5 to produce an output signal.

FIGS. 11a and 11b show details of highs intraframe averager 38 of FIG.1a. Highs averager 38 includes an input horizontal lowpass filter 1110with a cut-off frequency of approximately 1.5 MHZ, which receives signalC/SL. A low frequency component of input signal C/SL is produced at theoutput of filter 1110, and a high frequency component of input signalC/SL is produced at the output of a subtractive combiner 1112 arrangedas shown. The low frequency component is subjected to a 262H delay by aunit 1114 before being applied to an adder 1120. The high frequencycomponent of signal C/SL is processed by a V-T filter 1116 before beingapplied to adder 1120 for producing signal N.

Filter 1116 is shown in FIG. 11b as including a pair of 262H delayelements 1122 and 1124 and associated multipliers 1125, 1126 and 1127with associated weighting coefficients a1, a2 and a3. The multiplieroutputs are applied to an adder 1130 for producing a C/SL highs timeaveraged signal. Weighting coefficient a2 remains constant, butcoefficients a1 and a3 alternate between 1/2 and 0 from one field to thenext. Coefficient a1 exhibits values of 1/2 and 0 when coefficient a3exhibits values of 0 and 1/2.

FIG. 12 illustrates raster mapping apparatus which can be used for thetime expanders and compressors of FIGS. 6 and 7. In this regard,reference is made to the waveforms of FIG. 12a which illustrates themapping process. FIG. 12a shows an input signal waveform S with a centerportion between pixels 84 and 670 which is intended to be mapped intopixel locations 1-754 of an output waveform W by means of a timeexpansion process. End point pixels 1 and 670 of waveform S map directlyinto end point pixels 1 and 754 of waveform W. Intermediate pixels donot map directly on a 1:1 basis due to the time expansion, and in manycases do not map on an integer basis. The latter case is illustratedwhen, for example, pixel location 85.33 of input waveform S correspondsto integer pixel location 3 of output waveform W. Thus pixel location85.33 of signal S contains an integer part (85) and a fractional part DX(.33), and pixel location 3 of waveform W contains an integer part (3)and a fractional part (0).

In FIG. 12, a pixel counter operating at a 4×fsc rate provides an outputWRITE ADDRESS signal M representative of pixel locations (1 . . . 754)on an output raster. Signal M is applied to PROM (Programmable Read OnlyMemory) 1212 which includes a look-up table containing programmed valuesdepending upon the nature of raster mapping to be performed, eg.,compression or expansion. In response to signal M, PROM 1212 provides anoutput READ ADDRESS signal N representing an integer number, and anoutput signal DX representing a fractional number equal to or greaterthan zero but less than unity. In the case of a 6-bit signal DX (2⁶=64), signal DX exhibits fractional parts 0, 1/64, 2/64, 3/64 . . .63/64.

PROM 1212 permits expansion or compression of a video input signal S asa function of stored values of signal N. Thus a programmed value of READADDRESS signal N and a programmed value of fractional part signal DX areprovided in response to integer values of pixel location signal M. Toachieve signal expansion, for example, PROM 1212 is arranged to producesignal N a rate slower than that of signal M. Conversely, to achievesignal compression, PROM 1212 provides signal N at a rate greater thanthat of signal M.

Video input signal S is delayed by cascaded pixel delay elements 1214a,1214b and 1214c to produce video signals S(N+2), S(N+1) and S(N) whichare mutually delayed versions of the video input signal. These signalsare applied to video signal inputs of respective dual port memories1216a-1216d, as are known. Signal M is applied to a write address inputof each of memories 1216a-1216d, and signal N is applied to a readaddress input of each of memories 1216a-1216d. Signal M determines whereincoming video signal information will be written into the memories, andsignal N determines which values will be read out of the memories. Thememories can write into one address while simultaneously reading out ofanother address. Output signals S(N-1), S(N), S(N+1) and S(N+2) frommemories 1216a-1216d exhibit a time expanded or time compressed formatdepending upon the read/write operation of memories 1216a-1216d, whichis a function of how PROM 1212 is programmed.

Signals S(N-1), S(N), S(N+1) and S(N+2) from memories 1216a-1216d areprocessed by a four-point linear interpolator including peaking filters1220 and 1222, a PROM 1225 and a two point linear interpolator 1230,details of which are shown in FIGS. 12b and 12c. Peaking filters 1220and 1222 receive three signals from the group of signals includingsignals S(N-1), S(N), S(N+1) and S(N+2), as shown, as well as receivinga peaking signal PX. The value of peaking signal PX varies from zero tounity as a function of the value of signal DX, as shown in FIG. 12d, andis provided by PROM 1225 in response to signal DX. PROM 1225 includes alook-up table and is programmed to produce a given value of PX inresponse to a give value of DX.

Peaking filters 1220 and 1222 respectively provide peaked mutuallydelayed video signals S'(N) and S'(N+1) to two-point linear interpolator1230 which also receives signal DX. Interpolator 1230 provides a(compressed or expanded) video output signal , where output signal W isdefined by the expression

    W=S'(N)+DX[S'(N+1)-S'(N)]

The described four-point interpolator and peaking functionadvantageously approximates a (sin X)/X interpolation function with goodresolution of high frequency detail.

FIG. 12b shows details of peaking filters 1220 and 1222, andinterpolator 1230. In FIG. 12b, signals S(N-1), S(N) and S(N+1) areapplied to a weighting circuit 1240 in peaking filter 1220 where thesesignals are respectively weighted by peaking coefficients -1/4, 1/2 and-1/4. As shown in FIG. 12c, weighting circuit 1240 comprises multipliers1241a-1241c for respectively multiplying signals S(N-1), S(N) and S(N+1)with peaking coefficients -1/4, 1/2 and -1/4. Output signals frommultipliers 1241a-1241c are summed in an adder 1242 to produce a peakedsignal P(N), which is multiplied by signal PX in multiplier 1243 toproduce a peaked signal which is summed with signal S(N) in adder 1244to produce peaked signal S'(N). Peaking filter 1222 exhibits similarstructure and operation.

In two point interpolator 1230, signal S'(N) is subtracted from signalS'(N+1) in a subtractor 1232 to produce a difference signal which ismultiplied by signal DX in a multiplier 1234. The output signal frommultiplier 1234 is summed with signal S'(N) in an adder 1236 to produceoutput signal W.

Details of averager-differencer unit 1324 are shown in FIG. 15. SignalNTSCF is low pass filtered by unit 1510 to produce a "LOWS" componentwhich is subtractively combined with signal NTSCF in a unit 1512 toproduce the "HIGHS" component of signal NTSCF. This component isaveraged (additively combined) and differenced (subtractively combined)by a unit 1513 to produce an averaged highs component NH at an averagingoutput (+), and signal M at a differencing output (-). Component NH issummed in an adder 1514 with a 262H delayed output signal from filter1510 to produce signal N.

FIG. 16 shows details of unit 1513 in FIG. 15. FIG. 16 is similar to thearrangement of FIG. 11b previously discussed, except that inverters 1610and 1612 and an adder 1614 have been added as shown.

In FIG. 17, which shows details of unit 1330 of FIG. 13, signal Z isapplied to a side-center separator (demultiplexer) 1710 which providesseparated luminance highs sides and center signals YHO and YHErespectively, which were compressed and expanded at the encoder of FIG.1a. These signals are time expanded and time compressed by units 1712and 1714 using mapping techniques already discussed, to produceluminance highs sides and center signals YHS and YHC which are splicedby a unit 1716 (e.g., as can be accomplished by the system of FIG. 14)before being applied to amplitude modulator 1332.

In FIG. 18 an H-V-T bandpass filter 1810, which has the configuration ofFIG. 10c and a passband of 3.58±0.5 MHz, passes signal NTSCH to asubtractive combiner 1814, which also receives signal NTSCH after beingpassed through a transit time equalizing delay 1812. Separated luminancehighs signal YH appears at the output of combiner 1814. The filteredNTSCH signal film filter 1810 is quadrature demodulated by a demodulator1816 in response to chrominance subcarrier signal SC for producingchrominance highs IH and QH.

In FIG. 19, signals YN, IN and QN are separated into compressed sidepanel lows YO, IO, QO and into expanded center panel signals YE, IE, QEby means of a side-center panel signal separator (time de-multiplexer)1940. Demultiplexer 1940 can employ the principles of demultiplexer 816of FIG. 8 discussed previously.

Signals YO, IO and QO are time expanded by a side expansion factor(corresponding to the side compression factor in the encoder of FIG. 1a)by means of a time expander 1942 to restore the original spatialrelationship of the side panel lows in the widescreen signal, asrepresented by restored side panel lows signals YL, IL and QL.Similarly, to make room for the side panels, center panel signals YE, IEand QE are time compressed by a center compression factor (correspondingto the center expansion factor in the encoder of FIG. 1a) by means of atime compressor 1944 to restore the original spatial relationship of thecenter panel signal in the widescreen signal, as represented by restoredcenter panel signals YC, IC and QC. Compressor 1944 and expander 1942can be of the type shown in FIG. 12 discussed previously.

Spatially restored side panel highs YH, IH and QH are combined withspatially restored side panel lows YL, IL and QL by a combiner 1946 toproduce reconstructed side panel signals YS, IS and QS. These signalsare spliced to reconstructed center panel signal YC, IC and QC by meansof a splicer 1960 to form a fully reconstructed widescreen luminancesignal YF' and fully reconstructed widescreen color difference signalsIF' and QF'. Splicing of the side and center panel signal components isaccomplished in a manner which virtually eliminates a visible seam atthe boundary between the center and side panels, as will be seen fromthe subsequent discussion of splicer 1960 shown in FIG. 14.

In FIG. 20, interlace signals IF' (or QF') are delayed 263H by anelement 2010 before being applied to an input of a dual port memory2020. This delayed signal is subjected to an additional 262H delay by anelement 2012 before being added with the input signal in adder 2014. Theoutput signal from adder 2014 is coupled to a divide-by-two network 2016before being applied to an input of a dual port memory 2018. Memories2020 and 2018 read data at an 8×fsc rate and write data at a 4×fsc rate.Outputs from memories 2018 and 2020 are applied to a multiplexer (MUX)2022 for producing output progressive scan signals IF (QF). Also shownare waveforms illustrative of the interlace input signal (two lines,with pixel samples C and X designated) and the progressive scan outputsignal comprising pixel samples C and X.

FIG. 21 illustrates apparatus suitable for use as converter 1350 forsignal YF' in FIG. 13. Interlaced signal YF' is delayed by elements 2110and 2112 before being combined in an adder 2114 as shown. The delayedsignal from element 2110 is applied to a dual port memory 2120. Anoutput signal from adder 2114 is coupled to a divide-by-two network2116, the output of which is added to signal YT in an adder 2118. Theoutput from adder 2118 is applied to a dual port memory 2122. Memories2120 and 2122 write at a 4×fsc rate and read at an 8×fsc rate, andprovide output signals to a multiplexer 2124 which develops progressivescan signal YF.

FIG. 14 depicts side panel-center panel splicing apparatus suitable foruse as splicer 1960 in FIG. 19, for example. In FIG. 14, the splicer isshown as comprising a network 1410 for producing full bandwidthluminance signal YF' from side panel luminance signal component YS andcenter panel luminance signal component YC, as well as an I signalsplicer 1420 and a Q signal splicer 1430 which are similar in structureand operation to network 1410. The center panel and the side panels arepurposely overlapped by several pixels, e.g. ten pixels. Thus the centerand side panel signals have shared several redundant pixels throughoutthe signal encoding and transmission process prior to splicing.

In the widescreen receiver, the center and side panels are reconstructedfrom their respective signals, but because of the time expansion, timecompression and filtering performed on the panel signals, several pixelsat the side and center panel boundaries are corrupted, or distorted. Theoverlap regions (OL) and corrupted pixels (CP; slightly exaggerated forclarity) are indicated by the waveforms associated with signals YS andYC in FIG. 14. If the panels had no overlap region, the corrupted pixelswould be abutted against each other, and a seam would be visible. Anoverlap region ten pixels wide has been found to be wide enough tocompensate for three to five corrupted boundary pixels.

The redundant pixels advantageously allow blending of the side andcenter panels in the overlap region. A multiplier 1411 multiplies sidepanel signal YS by a weighting function W in the overlap regions, asillustrated by the associated waveform, before signal YS is applied to asignal combiner 1415. Similarly, a multiplier 1412 multiplies centerpanel signal YC by a complementary weighting function (1-W) in theoverlap regions, as illustrated by the associated waveform, beforesignal YC is applied to combiner 1415. These weighting functions exhibita linear ramp-type characteristic over the overlap regions and containvalues between 0 and 1. After weighting, the side and center panelpixels are summed by combiner 1415 so that each reconstructed pixel is alinear combination of side and center panel pixels

The weighting functions preferably should approach unity near theinnermost boundary of the overlap region, and should approach zero atthe outermost boundary This will insure that the corrupted pixels haverelatively little influence on the reconstructed panel boundary. Theillustrated linear ramp type weighting function satisfies thisrequirement. However, the weighting functions need not be linear, and anonlinear weighting function with curvilinear or rounded end portions,i.e. in the vicinity of 1 and 0 weight points, can also be used. Such aweighting function can readily be obtained by filtering a linear rampweighting function of the type illustrated.

Weighting functions W and 1-W can be readily generated by a networkincluding a look-up table responsive to an input signal representativeof pixel positions, and a subtractive combiner. The side-center pixeloverlap locations are known, and the look-up table is programmedaccordingly to provide output values from 0 to 1, corresponding toweighting function W, in response to the input signal. The input signalcan be developed in a variety of ways, such as by a counter synchronizedby each horizontal line synchronizing pulse. Complementary weightingfunction 1-W can be produced by subtracting weighting function W fromunity.

FIG. 22 shows apparatus suitable for use as progressive scan tointerlace converter 17c for signal YF in FIG. 1a. FIG. 22 also shows adiagram of a portion of progressive scan input signal YF with samples A,B, C and X in a vertical (V) and temporal (T) plane indicated, as alsoshown in FIG. 2a. Proscan signal YF is subjected to a 525H delay viaelements 2210 and 2212 for producing relatively delayed samples X and Afrom samples B. Samples B and A are summed in an adder 2214 before beingapplied to a divide-by-two network 2216. An output signal from network2216 is subtractively combined in a network 2218 with sample X toproduce signal YT. Signal YT is applied to an input of a dual-portmemory 2222, and signal YF from the output of delay 2210 is applied toand input of a dual-port memory 2223. Both memories 2222 and 2223 readat a 4×fsc rate and write at an 8×fsc rate, for producing signals YF'and YT in interlace form at respective outputs.

FIG. 23 shows apparatus suitable for use as converters 17a and 17b inFIG 1a. In FIG. 23 proscan signals IF (or QF) is applied to a 525H delayelement 2310 before being applied to a dual port memory 2312 which readsat a 4×fsc rate and writes at an 8×fsc rate, for producing interlaceoutput signal IF' (or QF'). Also shown are waveforms illustrative of theproscan input signal with first and second lines associated with samplesC and X, and the interlace output signal (the first line with sample Cstretched at a H/2 rate). Dual port memory 2312 outputs only the firstline sample (C) of the input signal, in stretched form.

FIG. 24 shows details of unit 80. Signals X and Z are applied to addressinputs of non-linear amplitude compressors 2410 and 2412 respectively.Compressors 2410 and 2412 are programmable read-only memory (PROM)devices each including a look-up table containing programmed valuescorresponding to the desired non-linear gamma compression function. Thisfunction is illustrated by the instantaneous input vs. output responseadjacent to unit 2412. Compressed signals X and Z from data outputs ofunits 2410 and 2412 are applied to signal inputs of signal multipliers2414 and 2416 respectively. Reference inputs of multipliers 2414 and2416 receive respective alternate subcarrier signals ASC in mutuallyquadrature phase relationship, i.e., signals ASC are in sine and cosineform. Output signals from multipliers 2414 and 2416 are added in acombiner 2420 to produce quadrature modulated signal M. In the decoderarrangement of FIG. 13, compressed signals X and Z are recovered via aconventional quadrature demodulation technique, and complementarynon-linear amplitude expansion of these signals is performed byassociated PROMs with look-up tables programmed with valuescomplementary to the values of PROMs 2410 and 2412.

What is claimed is:
 1. A system for processing a television-type signal,comprising:means for providing a television-type signal containing imageinformation of a first type; means for providing an auxiliary signalcontaining auxiliary image information of a second type having low andhigh frequency image information portions; means for nonlinearlycompressing large amplitude excursions of said high frequency imageinformation portion of said auxiliary signal, substantially exclusive ofsaid low frequency image information; and means for combining said imageinformation of said first type and said compressed high frequencyinformation to produce a combined signal.
 2. A system according to claim1, and further includingmeans for time compressing said low frequencyinformation of said auxiliary signal.
 3. A system according to claim 1,whereinsaid compressing means exhibits a gamma function.
 4. A systemaccording to claim 1, whereinsaid information of said first type is amain panel component of a widescreen television signal; and saidinformation of said second type is a side panel component of awidescreen television signal.
 5. A system for receiving atelevision-type signal comprising a first component containing a firsttype of image information and an auxiliary second component containing asecond type of image information, said system includingmeans forseparating said first and second components; means for non-linearlyamplitude expanding high frequency information of said second componentsubstantially exclusive of low frequency information; and video signalprocessing means responsive to said first component and to said expandedhigh frequency information of said second component for producing animage representative video signal.
 6. A system according to claim 5,whereinsaid first component contains main panel image information of awidescreen television signal; and said second component contains sidepanel image information of a widescreen television signal.
 7. A systemaccording to claim 5, whereinsaid expanding means exhibits a gammafunction.
 8. A system according to claim 5, and further comprisingmeansfor time expanding low frequency information of said auxiliary secondcomponent.
 9. A system for processing a television-type signal,comprising:means for providing a television-type signal representativeof a widescreen image having side panel image information and main panelimage information, and an image aspect ratio greater than that of astandard television image, said system comprising: means responsive tosaid television signal for developing a first component comprisinginformation representative of a standard aspect ratio image; meansresponsive to said television signal for developing and auxiliary secondcomponent comprising auxiliary television image information; and meansfor non-linearly compressing large amplitude excursions of highfrequency information of said second component.
 10. A system accordingto claim 9, whereinsaid second component contains side panel imageinformation.
 11. A system according to claim 9, and furthercomprisingmeans for time compressing low frequency information of saidauxiliary second component into an image overscan region.
 12. A systemaccording to claim 9, whereinsaid non-linearly amplitude compressed highfrequency information of said second component modulates an alternatesubcarrier other than a chrominance subcarrier.
 13. A system accordingto claim 9, whereinsaid system includes means for developing anauxiliary third component comprising horizontal high frequency imagedetail information for producing enhanced image resolution; and saidsystem includes means for non-linearly compressing large amplitudeexcursions of said third component.
 14. A system according to claim 9,whereinsaid compressing means exhibits a gamma function.
 15. A systemaccording to claim 13, whereinsaid non-linearly amplitude compressedthird component modulates an alternate subcarrier other than achrominance subcarrier.
 16. A system according to claim 13, whereinsaidnon-linearly amplitude compressed second and third components quadraturemodulate an alternate subcarrier other than a chrominance subcarrier toproduce a modulated signal; said system includes means for combiningsaid modulated signal with said first component to produce a combinedsignal; and said system further includes means for modulating an RFcarrier with said combined signal.
 17. A system according to claim 13,whereinat least one of said compressed second and third componentsmodulates an alternate subcarrier other than a chrominance subcarrier.18. A system according to claim 13, whereinsaid third componentcomprises horizontal high frequency image detail informationsubstantially exclusive of horizontal low frequency image information.19. A system according to claim 9, whereinsaid television signal andsaid auxiliary signal are baseband signals.
 20. A system according toclaim 9, and further comprisingtelevision signal receiving meansresponsive to said first component and to said compressed secondcomponent; and means for nonlinearly amplitude expanding said secondcomponent.
 21. A system for receiving a television-type signalrepresentative of a widescreen image having side panel image informationand main panel image information, and an image aspect ratio greater thanthat of a standard television image; said television signal including afirst component containing information representative of a standardaspect ratio television image, and an auxiliary second componentcontaining auxiliary television image information; said systemincluding:means for non-linearly expanding high frequency amplitudeexcursions of said second component; and video signal processing meansresponsive to said first component and to said expanded high frequencyinformation of said second component for producing an imagerepresentative video signal.
 22. A system according to claim 21,whereinsaid second component contains side panel image information. 23.A system according to claim 22, and further comprisingmeans for timeexpanding low frequency information of said auxiliary second component.24. A system according to claim 21, whereinsaid television signalincludes an auxiliary third component comprising horizontal highfrequency image detail information for producing enhanced imageresolution; and said system includes means for non-linearly amplitudeexpanding said high frequency information of said third component.
 25. Asystem according to claim 21, whereinsaid expanding means exhibits agamma function.
 26. A system according to claim 24, whereinsaid thirdcomponent comprises horizontal high frequency image informationsubstantially exclusive of horizontal low frequency image information.27. A system for processing a television-type signal, comprising:asource of television-type signal representative of a widescreen imagehaving side panel image information and main panel image information,and an image aspect ratio greater than that of a standard televisionimage; means responsive to said television signal for producing anauxiliary signal containing auxiliary image information; means fornon-linearly compressing large amplitude excursions of horizontal highfrequency information of said auxiliary signal; means for producing anintermediated first signal modulated by said compressed auxiliary signalinformation; and means for producing an output second signal modulatedby image information derived from said main panel information and bysaid intermediate first signal.
 28. A system according to claim 27,whereinsaid auxiliary signal contains side panel information.
 29. Asystem according to claim 27, whereinsaid television signal containsadditional high frequency information for producing enhanced imageresolution relative to a standard television signal image; said systemincludes means for non-linearly compressing large amplitude excursionsof said additional high frequency information; and said intermediatefirst signal is additionally modulated by said compressed additionalhigh frequency information.
 30. A system according to claim 29,whereinsaid intermediate first signal is an alternate subcarrier otherthan a chrominance subcarrier quadrature modulated by said compressedauxiliary signal and by said compressed additional high frequencyinformation; and said output second signal is a radio frequency carrier.31. A system for receiving a television-type signal representative of awidescreen image having side panel image information and main panelimage information, and an image aspect ratio greater than that of astandard television image; said television signal comprising a firstsignal modulated by an auxiliary signal component containing auxiliaryimage information, and a second signal modulated by image informationderived from said main panel information and by said modulated firstsignal; said system comprisingmeans for demodulating said modulatedfirst and second signals to recover said auxiliary signal component andsaid image information derived from said main panel information; meansfor non-linearly amplitude expanding said recovered auxiliary signalcomponent; and video signal processing means responsive to saidrecovered derived image information and to said expanded recoveredauxiliary signal component to produce an image representative signal.32. A system according to claim 31, whereinsaid auxiliary signalcomponent contains side panel image information.
 33. A system accordingto claim 31, whereinsaid television signal contains additional highfrequency information for producing enhanced image resolution relativeto a standard television signal image; and said system includes meansfor non-linearly amplitude expanding said additional information.